1. Technical Field
The present disclosure relates to acoustic treatments for jet engines.
2. Description of Related Art
Acoustic treatments for jet engine exhaust are generally exposed to significant thermal gradients in the radial direction. These gradients are apparent for exhaust nozzles that are exposed to primary flow on one side, and fan flow on the other. They are also apparent for exhaust centerbodies that are internally vented, which are exposed to primary flow on one side and scavenged air on the other. These gradients are further apparent for any exhaust components at engine startup where the surfaces bounding the primary flow are at temperatures well in excess of the surrounding structure. This temperature differential can be in excess of 1000 degrees Fahrenheit. A thermal gradient of this magnitude can induce significant structural load. And due to the direction of the thermal gradient (away from the primary flow), this issue is critically important to the design of acoustic treatments on exhaust centerbodies.
One type of acoustic treatment includes an acoustic chamber that traps sound energy. The acoustic chamber lies beneath an outer perforated skin of the acoustic treatment. Existing designs limit the depth of the acoustic chamber to about one half inch, because as the depth of the acoustic chamber increases so does the thermal gradient across the chamber. Unfortunately, limiting the depth of the acoustic chamber also limits the range of frequencies that the chamber may attenuate. Accordingly, there is a need to increase the ability of acoustic chambers to withstand the stresses generated by thermal gradients so that the depths of the chambers may also be increased.